Blood pumps have been commonly used to provide mechanical support or assistance to the left ventricles of patients. Typically, the left ventricle is responsible for pumping blood into the aorta and throughout a majority of the patient's body. Ventricular assistance has been previously been provided by an implanted blood pump, such as the Ventrassist™ rotary blood pump described in U.S. Pat. No. 6,227,797—Watterson et al.
These blood pumps generally pump blood in parallel to the normal circulatory system by removing blood directly form the left ventricle and pumping into a portion of the aorta. Generally when such a blood pump is implanted, blood may flow or be pumped by both the left ventricle and the blood pump.
Previously, these rotary blood pumps have been operated at relatively constant speeds because of the design of the pump. In the past, some efforts have been made to adjust the pumping speed to compensate for under or over-pumping of the left ventricle. However, these types of control systems often fail to sufficiently mimic the natural cardiac cycle of a patient in which the circulatory system experiences a pulsed blood flow and/or pressure.
Previously, older blood pumps relied on compression type mechanisms to provide mechanical assistance to the heart and circulatory system. These compression type blood pumps generally include a sac member and two one-way valves arranged so as to provide pulsatile outflow to the patient's circulatory system. These devices are generally prone to mechanical failure as well as thrombogenesis or blood clotting occurring around the valves. An example of these types of pulsatile blood pumps is described within U.S. Pat. No. 5,728,069—Montevecchi et al. These types of cardiac assist devices are commonly classified as first generation assist devices.
U.S. Pat. No. 6,547,753—Plunkett et al describes a heart-lung machine that includes a blood pump. The described heart-lung machine wherein the steady state blood flow exiting the artificial lung is induced to become pulsatile by the use of an elastic bladder. However, the inclusion of a compressible bladder in this system may also be a location of potential thrombogenesis and is generally not preferred for patient safety.
U.S. Pat. No. 4,296,500—Monties et al describes a rotary blood pump that may provide a pulsatile flow by the use of a rotary piston shaped like a eccentric ovoid. The rotation of the rotary piston in this pump causes the blood passing through the pump to be ejected in a pulsed pattern whilst the piston is rotated at a steady rate. The main disadvantage with this system it that the depicted configuration may subject the blood to relatively high pressures at the times of ejection and may cause haemolysis to occur the blood.
U.S. Pat. No. 4,957,504—Chardack discloses a rotary continuous flow blood pump in which the pumping speed is ramped between two preferred settings and is synchronised with either ECG data or other data from additional implanted sensors. The main disadvantage with this arrangement is that the use of additional implanted sensors increase the patient's risk of infections, complications and blood clotting.
The present invention aims to or at least address or ameliorate one or more of the disadvantages associated with the abovementioned prior art.